9,874 research outputs found
Accretion Into and Emission from Black Holes
No full textAnalyses are given of various processes involving matter falling
into or coming out of black holes.
A significant amount of matter may fall into a black hole in a
galactic nucleus or in a binary system. There gas with relatively high
angular momentum is expected to form an accretion disk flowing into the
hole. In this thesis the conservation laws of rest mass, energy, and
angular momentum are used to calculate the radial structure of such a
disk. The averaged torque in the disk and flux of radiation from the
disk are expressed as explicit, algebraic functions of radius.
Matter may be created and come out of the gravitational field of
a black hole in a quantum-mechanical process recently discovered by
Hawking. In this thesis the emission rates of massless particles by
Hawking's process are computed numerically. The resulting power spectra
of neutrinos, photons, and gravitons emitted by a nonrotating hole are
given. For rotating holes, the rates of emission of energy and angular
momentum are calculated for various values of the rotation parameter.
The evolution of a rotating hole is followed as energy and angular
momentum are given up to the emitted particles. It is found that angular
momentum is lost considerably faster than energy, so that a black
hole spins down to a nearly nonrotating configuration before it loses a
large fraction of its mass. The implications are discussed for the lifetimes and possible present configurations of primordial black
holes (the only holes small enough for the emission to be significant
within the present age of the universe.
As an astrophysical application, a calculation is given of the
gamma-ray spectrum today from the emission by an assumed distribution
of primordial black holes during the history of the universe. Comparison
with the observed isotropic gamma-ray flux above about 100 MeV yields
an upper limit of approximately 10^4 pc^(-3) for the average number density
of holes around 5 x 10^(14)g. (This is the initial mass of a nonrotating
black hole that would just decay away in the age of the universe.) The
prospects are discussed for observing the final, explosive decay of an
individual primordial black hole. Such an observation could test the
combined predictions of general relativity and quantum mechanics and
also could provide information about inhomogeneities in the early universe
and about the nature of strong interactions at high temperatures.</p
A PC parallel port button box provides millisecond response time accuracy under Linux
No full textFor psychologists, it is sometimes necessary to measure people's reaction times to the nearest millisecond. This article describes how to use the PC parallel port to receive signals from a button box to achieve millisecond response time accuracy. The workings of the parallel port, the corresponding port addresses, and a simple Linux program for controlling the port are described. A test of the speed and reliability of button box signal detection is reported. If the reader is moderately familiar with Linux, this article should provide sufficient instruction for him or her to build and test his or her own parallel port button box. This article also describes how the parallel port could be used to control an external apparatus
PC-DFA scores plots of FT-IR data for three different strains of <i>P</i>. <i>putida</i> strains upon propranolol shock.
No full textSymbols represent different strains. (A) P. putida DOT-T1E is the wild type (stars) and ten PCs with a total explained variance (TEV) of 99.43% were used for the DFA, (B) P. putida DOT-T1E-PS28 is the mutant (closed triangles) and ten PCs with a TEV of 99.65% were used for the DFA, (C) P. putida DOT-T1E-18 is the mutant (closed circles) and ten PCs with a TEV of 99.03% were used for the DFA. Colour coding: control with no propranolol (red), cells exposed to 0.2 mg mL-1 propranolol (black), 0.4 mg mL-1 propranolol (brown), and 0.6 mg mL-1 propranolol (blue). Arrows indicate the direction of shift because of the increase of propranolol concentration. (D) PC-DFA loadings plot for P. putida DOT-T1E. (E) PC-DFA loadings plot for P. putida DOT-T1E-PS28, (F) PC-DFA loadings plot for P. putida DOT-T1E-18. Significant loadings were assigned to bacterial proteins.</p
PC-based single-vessel flow velocity (CBFv) mapping.
No full text(A) Representative 2D MGE slices (yellow boxes) from a deep layer of the primary forepaw somatosensory cortex (first frame) at different TEs, as indicated. (B) The 2D A–V map (yellow box) derived from the images with different TEs in panel A, arterioles, and venules appear as bright and dark voxels, respectively. The expanded views (red boxes) show individual venules, i.e., black voxels marked in blue, and arterioles, i.e., white voxels marked in red. (C) The vectorized flow velocity map (blue box) from the same 2D MGE slice in panel B. The expanded views (green boxes) show the individual venules, i.e., white dots with positive velocity, and arterioles, i.e., black dots with negative velocity. Note that 2 bright dots are caused by the “overflowed” velocity beyond the maximal velocity, i.e., the Venc parameter, defined in the PC-MRI sequence, which could be not correctly estimated. (D) Scatter plot of the flow velocities from individual arterioles and venules as the function of the normalized signal intensities of each vessel in the A–V map of panel B, data from 11 rats as indicated. Insert shows the blood flow direction of arterioles and venules in the forepaw somatosensory cortical region. The lower panel shows the histogram of the blood velocity distribution across arterioles and venules, as well as the bar graph to show the mean velocity. The data underlying this figure can be found in S2 Data. A–V, arteriole–venule; CBFv, cerebral blood flow–related velocity; MGE, multi-gradient echo; PC, phase contrast; ROI, region of interest; Venc, velocity encoding; TE, echo time.</p
Millisecond accuracy video display using OpenGL under Linux
No full textTo measure people’s reaction times to the nearest millisecond, it is necessary to know exactly when
a stimulus is displayed. This article describes how to display stimuli with millisecond accuracy on a
normal CRT monitor, using a PC running Linux. A simple C program is presented to illustrate how this
may be done within X Windows using the OpenGL rendering system. A test of this system is reported
that demonstrates that stimuli may be consistently displayed with millisecond accuracy. An algorithm
is presented that allows the exact time of stimulus presentation to be deduced, even if there are relatively
large errors in measuring the display time
Frontmatter (Titlepage, Table of Contents, Author List, PC List, Reviewer List)
No full textFront matter including table of contents, author list, PC list, and reviewer list
Papaya black seeds have beneficial anticancer effects on PC-3 prostate cancer cells
No full textAim: The study investigated the effect of papaya seeds on prostate cancer (PC) using PC-3 cell line because papaya seeds have effects on the male reproductive system notably decreasing sperm concentration, motility, and viability, leading to azoospermia after short-to-long-term treatment.Methods: The black seeds from yellow (ripe) papaya and white seeds from green (unripe) papaya were harvested and then extracted in water, 80% methanol, and hexane. The cytotoxic effects of seeds extracts were determined using a WST-1 proliferation assay. The amount of total polyphenols was determined using Folin Ciocalteu reagent.Results: The methanol extracts from black seeds significantly (P < 0.05) decreased cell proliferation of PC-3 cells whereas hexane- and water-extracts have no effect. However, the water-extract from white seeds stimulated PC cell proliferation. The black seeds contained significantly more polyphenols than that of white seeds. The data suggest that black seeds from papaya have anticancer effects on PCs whereas white seeds stimulated prostate cancer proliferation. The anticancer effect of black seeds may be because of their high concentration of polyphenols.Conclusion: The black seeds from papaya may have a potential to reduce growth of prostate cells; however, consumption of white seeds should be avoided as they may stimulate pre-existing prostate cancer
A structured PC-PATR grammar editor and application to Bahasa Indonesia
No full textThis thesis describes the development of a structured editor for grammar files for the PC-PATR syntactic parsing program and an analysis tool for its output called PC-PATR-EDITOR. It describes the difficulties with authoring plain text grammar files and reading the parser\u27s output. The editor solves these problems by providing an editing environment where users do not have to remember the file\u27s syntax, where users can only input content valid at the point of editing, and by processing the parser\u27s output and displaying it in ways familiar to most linguists. The paper contains three case studies that illustrate PC-PATR-EDITOR\u27s usefulness by implementing a grammar fragment for Bahasa Indonesia. It offers critiques and suggestions for future improvements for the editor and analysis tool.
PC-PATR-EDITOR is available for public use: sil.org/resources/archives/9470
High efficiency implementation of PC and PC stable algorithms yields three-dimensional graphs of information flow for the Earth' atmosphere
No full textSeptember 3, 2014.Causal discovery algorithms have recently been applied to several climate applications. In particular, in prior work we have developed methods to recover pathways of interaction in the global climate system, using the classic PC algorithm. However, standard implementations of the PC algorithm cannot handle the large number of variables and temporal models required for this application. This technical report shows that a more efficient implementation of the PC algorithm can provide speed gains of a factor of 1,000 or more. This in turn enables us to calculate graphs of information flow with much higher resolution grids. Furthermore, we can now - for the first time ever - calculate information flow graphs that extend over three dimensions, i.e. rather than just including one layer of the planet's atmosphere we can now capture interactions across several height layers
Pedigrees of the seven large PC families.
No full textSolid black rectangles represent affected patients with PC. Patients with PC analyzed by exome-seq were numbered (from 01 to 22). PC, prostate cancer.</p
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